Field of the Invention
The invention provides UV-absorbing polymers. The invention further provides a wide variety of formulations comprising the UV-absorbing polymers.
Description of Related Art
It is now generally accepted that ultraviolet (UV) radiation can be a serious health hazard. Even a limited exposure to solar radiation can cause short- and long-term skin damage, such as erythema, burns, wrinkles, lentigo (“liver spots”), skin cancers, keratotic lesions, and other cellular changes. There is a greater risk for developing such conditions for those who send prolonged time in the sun, such as for their occupation or during recreation.
UV radiation is just one portion of the electromagnetic spectrum with wavelengths from about 100 nm and about 400 nm, and is further divided into three subregions. UV-A radiation, from about 320 nm to about 400 nm, has the longest wavelength within the UV spectrum, and consequently is the least energetic. While UV-A rays can induce skin tanning, they are liable to induce adverse changes as well, especially in the case of sensitive skin or of skin which is continually exposed to solar radiation. In particular UV-A rays cause a loss of skin elasticity and the appearance of wrinkles, leading to premature skin aging. UV-B rays have shorter wavelengths, from about 290 nm to about 320 nm, and their higher energy can cause erythema and skin burns which may be harmful. The third subgroup, UV-C has the shortest wavelengths, from about 200 nm to about 290 nm, and the highest energy. The Earth's ozone layer effectively filters much UV-C radiation from reaching the ground. Nonetheless, UV-C rays can be generated from tanning bed devices.
In addition to harming the skin, UV radiation can injure the hair, resulting in color changes (especially for color-treated hair), embrittlement, and a loss in aesthetics (e.g., shine, manageability).
UV radiation damage is not limited to the skin and hair, as inanimate objects exposed to solar radiation can experience changes related to color, hardness, and structural integrity, which can contribute to aesthetical and functional deterioration. Thus, there is the very real and demanding need for compositions that protect the skin, hair, and objects from UV rays, especially UV-A and UV-B radiation. Of special interest are compositions that provide broad UV-spectrum protection from both UV-A and UV-B radiation.
Broadly speaking, para-aminobenzoic acid (PABA) exhibits a common trait shared with many UV absorbers/filters. The molecule possesses both electron withdrawing and electron accepting groups, providing resonance delocalization that coincides with the absorbed energy of UV radiation:

However, PABA is a highly polar molecule, making it water soluble, and giving it low persistence, meaning that it is not highly retained on the skin after swimming or perspiring. In addition, due to extensive intermolecular bonding, PABA exists as a solid, which may further complicate its formulation. Thus, there exists the need to improve the persistence of UV absorbers, especially those that are water-soluble, and to provide formulation flexibility.
UV absorbers may exhibit photolability, in which the absorbed energy causes photodegradation and/or photoreactivity, and thus reduce its efficacy. Such photolability may result from irreversible isomerisms (i.e., keto-enol tautomerism and cis-trans isomerism), photocleavage, and/or photoaddition, and may be formulation sensitive, (e.g., blends of avobenzone and octinoxate). Examples of photolabile UV absorber include, without limitation: avobenzone, PABA derivatives, cinnamates, and dibenzoyl methane derivatives, all of which degrades over time, and reduce UV protection. Hence, there exists a need to stabilize UV absorbers from photodegradative effects.
Additionally, there exists the need to enhance the efficacy of UV absorbers without increasing their content in the formula, since a maximum addition level frequently is regulated. This efficacy need is especially important for avobenzone, a highly effective UV-A absorber. Avobenzone is subject to keto-enol isomerization due to formulation dependencies (e.g., solvent, other UV absorbers):

The enol tautomer (left) has its maximum absorbance at 357 nm, which identifies it as a UV-A absorber. Unfortunately, avobenzone is subject to bimolecular reactions (viz, via cleavage mechanisms) that alter the molecule's structure and decrease its effectiveness as an UV absorber. Hence, an effective method is needed for stabilizing labile chromophores like avobenzone in order to enhance their efficacy without increasing their addition level.
Methods for stabilizing chromophores, and in particular UV absorbers, are known in the prior art. For example, Japanese patent 1971/26,860 describes UV stabilizers having amino, hydroxyl, or isocyanate groups attached to crosslinked polymers, being crosslinked glycidyl methacrylate-divinylbenzene copolymers or crosslinked styrene-maleic anhydride-divinylbenzene copolymers.
U.S. Pat. No. 4,868,246 teaches polymer chemistries having UV absorbers bonded to recurring units:
in the polymer backbone, on grafted side chains, as pendant units, or as combinations thereof. The group N-G is the residue of a primary amino or hydrazido substituted stabilizer group selected from (a) 2-hydroxybenzophenones, (b) 2-(2-hydroxyphenyl)-2H-benzotriazoles, (c) aryl salicylates, or (d) oxalic acid amides. The polymeric stabilizers are directed for use in other polymeric systems which are normally subject to actinic light degradation, for example polypropylene. No mention is made of their use in personal care compositions.
A similar approach is taught in U.S. Pat. No. 4,857,596 for thermally stabilizing antioxidants.
Polymer-bound light stabilizers are disclosed in U.S. Pat. No. 4,975,494 that are prepared from a preformed polymer having two different types of reactive groups and a light stabilizer having hydrazido functionality.
U.S. Pat. No. 6,569,531 teaches additive-containing resins having a bi- or multifunctional additive linking a polyester resin with an additive, such as a UV absorber.
U.S. Pat. No. 7,648,697 teaches compounds derived from polyanhydride resins with film-forming, UV-absorbing, and photostabilizing properties.
Japanese patent 1985/84,378 provides 2-hydroxy-4-(2-hydroxyethoxy)benzophenone reacted with maleic anhydride-grafted polyethylene to form a polyethylene-bound 2-hydroxybenzophonone semi-ester.
Two radiation-absorbing polymer chemistries are taught in U.S. Pat. No. 6,255,405. The '405 patent is directed toward radiation-absorbing compositions and coatings, particular for “forming a bottom anti-reflective coating upon producing an integrated circuit.” The polymeric compositions comprise two recurring units, the first having the formula:
wherein Ra and Rb may be the same or different and represent hydrogen, an alkyl group or other organic groups, Ar represents an organic chromophore, and n represents 0 or an integer of 1 or more; and the second recurring unit having the formula:
wherein Rc and Rd may be the same or different and each represents hydrogen, an alkyl group, a carboxyl group, or other organic groups, and Z represents hydrogen, a substituted or non-substituted alkoxyl group, a substituted or non-substituted alkyl group, a halogen atom, —CN, an alkylcarbonyloxy group, an imide group, a substituted or non-substituted carbamoyl group, a substituted or non-substituted oxycarbonyl group, or a substituted or non-substituted phenyl group.
U.S. Pat. No. 6,492,455 discloses compositions comprising the reaction product of a C6+ alpha olefin/maleic anhydride copolymer with a polyfunctionalized secondary or tertiary amine. The resulting copolymer is an alternating copolymer of an olefinic monomer and a maleic anhydride with a polyfunctionalized secondary or tertiary amine. Uses includes hair spray and water-proof sunscreen compositions
U.S. Pat. No. 7,361,710 describes compositions comprising the reaction of (a) an unsaturated vegetable oil and an enophile or dienophile having acid, ester, or anhydride functionality and (b) a functional vinyl monomer. For example, soybean oil is reacted with maleic anhydride, to yield a maleated vegetable oil:
The maleated oil is reacted with hydroxyethyl methacrylate, 2-(tert-butylamino)ethyl methacrylate, or glycidyl methacrylate.
Another maleated oil is described in U.S. Pat. No. 3,428,589, which is directed to polycarboxylic acid anhydride resins of high viscosity, and for such resins of voltage capabilities. This invention discloses the heating (1) of a dry oil, a modified drying oil, or a mixture thereof, and (2) and alpha, beta-ethylenically unsaturated dicarboxylic acid anhydride, which is heated until a polycarboxylic acid anhydride resin product (i.e., an adduct) with a desirably high viscosity is obtained. The polycarboxylic acid anhydride resin is then reacted with an organic aromatic primary or secondary amine, as represented in the following reaction:
wherein R′ represented the drying oil portion of the adduct, and R″ is hydrogen or alkyl. The '589 patent specifies that the organic aromatic primary or secondary amine has from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms. The '589 patent discloses compositions for electrocoating baths, compositions with high throwing power, and of excellent intermediate voltage capacity.
Additional disclosure related to anhydride-functionalized vegetable oils is provided by Aydin, S., et al., Prog Org Coat, 51, 273-279, 2004; and by Guner, F. S., et al., Prog Polym Sci, 31, 633-670, 2006, both of which are incorporated in their entirety by reference. While these works describe methods to graft anhydride functional groups onto vegetable oils, they do not teach subsequent grafting of UV absorbers onto the anhydride moiety.
Functionalized poly(alpha olefin-maleic anhydride) polymers are the subject of application WO 2007/096400A1. This functionalized copolymer has the structure:
wherein X is —O— or —NH—, and —X—R2— is a functional radical selected from a group that includes natural molecules that are UV absorbers, such as tannins, flavonoids, thymol, caffeic acid esters, and vitamin E.
UV absorbers bound to polymers in personal care compositions are taught in US 2010/0189661, the contents of which are incorporated in their entirety by reference.
Despite advances in UV-absorbers, there remains a commercial demand for UV-absorbing polymers with enhanced performance.